Removal of coatings



Sept. 30, 1958 w. s. PAJES REMOVAL 'OF COATINGS Filed Dec. 5, 1955 )NVENTOR m E I N m m T s T W A REMOVAL OF COATINGS Wolf Szmul Pajes, New York, N. Y.

Application December 5, 1955, Serial No. 550,928

8 Claims. (Cl. 134-15) This invention relates to the art of removing coatings from carriers, such as motion picture film or the equivalent, without damaging the carriers, the coatings including man-made coatings or naturally acquired coatings, such as parafiin, rust, scalings, sediment, and patine.

Various methods have been employed for removing layers of material adhering to a carrier or base. Chief among these is the use of a solvent for the coating material, the carrier and coating being dipped in the solvent whereupon the coating is dissolved and the carrier emerges free of the coating. If the material of the coating and the solvent are worth reclaiming, this method involves complicated procedures for separating the solvent from the coating material.

It is the principal object of the invention to provide a process of removing the bulk of the coating Without the use of solvents and in which the coating material may be easily reclaimed in a simple and expeditious manner.

Another object of the invention is to provide a process of removing coatings which may be carried out in two steps, either performed in rapid succession or with an indeterminate time separation.

Another object of the invention is to provide a process of removing coatings comprising two steps which may be carried out simultaneously.

Another object of the invention is to provide a process of removing the bulk of paraffin coating from motion picture film without the use of solvents.

, One embodiment of the invention is illustrated in the single figure in which apparatus for carrying on a continuous coating-removal process is disclose Broadly the invention comprises exposing the coated carrier for a predetermined period of time to a temperature at which the difference in coeflicients of linear expansion of the materials of the carrier and coating is such as to cause the coating to crack into a multitude of separate, tiny particles which'are shifted and loosened with respect to the carrier, and then subsequently removing the loosened particles of the coating by mechanical means.

Subjecting the carrier and coating to a rise in temperature may be objectionable where heat might tend to cause damage to the carrier itself, or soften or melt the coating. In such cases the temperature of the carrier and coating must be lowered for a period of time and to such a degree as to produce the desired efiect.

This process is especially suitable and advantageous in the removal of protective paralfin coatings from motion picture film. Such a coating is applied to motion picture film for the purpose of impressing explanatory subtitles in accordance with the teachings of the Hruska Patent No. 2,051,603. In the process disclosed in this patent, the film to be titled is coated with a protective layer of paraffin, the letters of the subtitles are impressed in the parafiin coating so as to form a stencil, the entire film is immersed in a solution which etches out or bleaches the material in the spaces of the letters, and then the film is immersed in a solvent which dissolves the parafiin Patented Sept. 30, 1958 ice coating, leaving the film clean. In this process a very elaborate, costly, andv tedious procedure of distillation must be carried out to separate the parafiin from the solvent if the solvent and parafiin are to be reclaimed for re-use.

In using the process of the present invention to remove the paraffin coating from the film after subtitles have been applied as in the Hruska patent, I subject the parafiin-coated film to low temperatures for a period of time to chill it thoroughly. This may be done, for example, by dipping it in liquid nitrogen. When the film is removed from the liquid nitrogen, the parafiin coating will be found to be cracked and loosened. Actually the material is broken up into a multitude of tiny, discrete, particles which have shifted and have become loosened from the film base because of the difference in the linear expansion coefficients. A blast of compressed air against the film will blow these particles awayin the form of a flaky dust and leave the film substantially free of the paraflin coating. v

The temperature necessary for carrying out the invention will have to be determined by experiment for different sets of materials, since all materials have different coefiicients of linear expansion and a temperature suitable for one set of materials may not be effective with another set. 7

Obviously what is happening in this process is that the chilled film-parafiin structure undergoes a violent contraction. The degree of contraction, however, difiers sufficiently for the film and coating so as to cause a structural shift effecting the cracking and loosening of the paraflin. I

In a series of experiments performed with liquid nitrogen on paraifin coated motion picture film, the following has been observed and established:

A. For a strip of film, a one to two second dip in liquid nitrogen is sufiicient to cause the required cracking and loosening of the parafiin'coating.

B. A short blast of air under compression of five pounds per square inch against the film removed prac tically all the parafiin in the form of a snow-like dust.

C. A time interval of as much as ten minutes between steps A and B did not afiect the effectiveness of the process. This means that the exposure of the coated film to room temperature after step A does not cause the parafiin to readhere to the film.

D. The chilling process does not affect the emulsion and does not impair the quality of the film picture.

The observation pointed out under C is of great practical value as it permits the chilling of whole film reels in batches and the exposing of the film to the air blast process at a convenient time and place. This makes the whole method very practical and non-critical.

It is to be pointed out that the separation of the parafiin from the film is not effected by the contact with liquid nitrogen as such, but it is the chilling caused by the contact which accomplishes the separation of the layers. This brings up the possibility of joining steps A and B into one step, namely by providing a very cold blast of air directed against the paraffin coating. This would require, however, a large supply of very cold air which could be accomplished by blowing air across copper coils carrying liquid nitrogen for chilling it thoroughly and then directing it against the paraffincoated film.

It must be further pointed out that the chilling and air blast does not remove the parafiin completely. Upon inspection, specks of parafi'in can be seen here and there. Thus, the film has to go through a paraflin solvent cleaning operation. However, the amount of paraffin to be dissolved is negligibly small as compared with the amount of parafiin contained in the original coating. Hence the quantity of solvent needed, such as trichloroethylene, becomes comparatively very small.

One way of realizing the removal of the parafiin coating by the chilling process is to run the coated film through a bath of liquid nitrogen and on its emergence to blast air againstthe paraflin, the'operation being done in a box-like paraffin collector. Then from there, for final cleaning, the film would be run through a solvent bath, to remove traces of adhering paraffin, and from there through a water rinsing bath and a drying procedure.

Such a continuous process has been illustrated schematically in the singlefigure in which a heat-insulated vessel 1 contains a supply of liquid nitrogen 2. Paratfincoated motion picture film .3 is continuously passed through the liquid nitrogen, moving over rollers 4 rotatably positioned above the vessel and under rollers :5 rotatably positioned within the vessel. The film is moved by any suitable means, not shown.

.The film, thus chilled, then passes through the paratfin collector 6, moving over rollers 7 above the collector and under rollers 8 within the collector. A nozzle 9, connected to a source of compressed air, not shown, is positioned within the collector 6 to direct a blast of air against the film in order to remove the parafiin. The film may then pass into a tank 10 containing a solvent 11 for the paraflin. The film is guided, as before, over rollers 12 above the tank and under rollers .13 within the tank. The solvent removes any remaining parafiin after which the film passes through a tank 14 containing water 15, being guided by upper and lower rollers 16 and 17. The film then is dried, as by passing it through a suitable drying oven 18.

Another way of carrying out this invention is to chill batches of film reels in a bath of liquid nitrogen and then in a separate operation blast with air, dissolve the remainder of the parafiin with a solvent, .rinse, and dry.

Still another manner of performing the invention is to provide a continuous blast of chilled air in accordance with the principle of adiabatic decompression, which, asis well known, lowers thetemperature of the decompressed gas according to the thermodynamic relation:

where T is the temperature, K is a constant for the-particular gas, C is a constant, and P is the pressure of the gas. The film is placed in this blast of chilled air and the steps of loosening and removing the coating are carried on simultaneously.

What .I. claim is:

l. A process of separating a protective paraffin coating from a motion picture film which comprises chilling the coated film to such a temperature that the wax-like coating is broken up into discrete particles which are loosened from the film and removing the particles thus loosened.

2. A process of separating and removing a protective paratfin coating from a motion picture film, as defined in claim 1, in which the step of lowering the temperature of the coated film comprises immersing the coated film in a liquified gas.-

3. A process of separating and. removing a protective parafiin coating from a motion picture film, as defined in claim 2, in which the liquified gas is liquid nitrogen.

4. A process of separating a parafiin coating from a motion picture film, as defined in claim 1, in which the step of removing the particles of the coating is performed by blowing a stream of air against the film.

5. A process of separating andremoving a protective paraflin coating from a motion picture film which com- .prises immersing the coated film in liquid nitrogen to crack and loosen particles of the paraffin, directing a blast of air against the coated film to remove the loosened parafiin particles, immersing the film in a paratfin solvent to remove any remaining parafiin, and removing the solvent from the film.

'6. A continuous process of separating a protective paratfin coating from a motion picture film which com- :prisespassing the coated film continuously first through a bath of liquified gas and then through a blast of air. 7. A continuous process of separating a protective parafiin coating from a motion vpicture film which oomprises passing the coated film first through a chilling bath of liquid nitrogen to crack and loosen particles of the paraffin coating, then through a blast of air to remove the loosened parafiin particles, then through a parafiin solvent to remove the remaining paratfin, then through a water'rinsing bath to remove any adhering solvent.

8. A process of separating and removing a parafiin coating from a motion picture film to which it adheres, as defined in claim 1, in which the steps are carried out simultaneously.

References Cited in thefile of this patent UNITED STATES PATENTS 661,873 Hopcroft Nov. 13, 1900 855,210 Stewart May 28, 1907 2,357,695 Skowron Sept. 5, 1944 

1. A PROCESS OF SEPARATING A PROTECTIVE PARAFFIN COATING FROM A MOTION PICTURE FILM WHICH COMPRISES CHILLING THE COATED FILM TO SUCH A TEMPERATURE THAT THE WAX-LIKE COATING IS BROKEN UP INTO DISCRETE PARTICLES WHICH ARE LOOSENED FROM THE FILM AND REMOVING THE PARTICLES THUS LOOSENED. 